In general, an assembled battery such as a lithium ion battery in which a plurality of battery cells (electrical storage devices) are connected in series is used as a large capacity high output battery to drive a motor of a hybrid vehicle or an electric vehicle, or the like. In the assembled battery, a monitoring circuit may be used to monitor and control a voltage of each of the battery cells.
Monitoring circuits are connected in multiple stages through wiring such as a flat cable. Such wiring may be disconnected depending on an insertion state, or the like, but conventionally, a disconnection fault cannot be detected.